Mike,

I don't want to get into a long-drawn-out debate about the
relationship between hummingbird migration and flowering shrubs, which
probably could not be resolved without a lot more data collection.
However, I believe you are quite incorrect when you say "in the case
of hummingbirds, the northern movement, latitude by latitude, is ahead
of most bud burst".

The dates you cite for first arrivals (Feb 6 to Feb 21) are for
the EARLIEST individuals each year. Yes, it may well be that some
hummers arrive before flower nectar is available (or many insects),
and these individuals may be at great risk of perishing. There are
lots of accounts in the literature of mass starvation of
early-arriving Tree Swallows and Purple Martins, when their arrival
coincided with, or was shortly followed by, a cold snap that
temporarily wiped out flying insects. I have witnessed such mortality
myself in Purple Martins during February in Mississippi.

You have said nothing so far about when the bulk of the Rufous
Hummingbird population arrives in Oregon. I suspect that, as in B.C.,
it is at least 6 weeks after the first birds arrive, which would put
it into late March or early April, if not later. By then, I would be
surprised if there were not abundant salmonberry, currant, and other
flowers available.

Campbell et al. in "The Birds of B.C." list only one Rufous
Hummingbird record for B.C. in February. That was on Feb. 28, 1988.
Significantly, the bird was reported to have died of cold and is now a
specimen. The Feb. 25 record that I mentioned for Vancouver was in
1999. Campbell et al. cite a total of 264 March records of Rufous
Hummingbird for B.C., versus almost 2500 in April. From that, I would
conclude that not much more than 10% of the population has arrived by
March 31st in most years.

You speak as if both flowering dates of plants and migration dates
of birds were determined by photoperiod (daylength), and only
incidentally related to each other. First of all, both flowering dates
and arrival dates can vary by 2-3 weeks from one year to the next,
depending on temperature and other weather factors, so photoperiod is
not the only governing factor. Secondly, there is a powerful
evolutionary connection between hummingbirds and some flowering
shrubs, which tends to synchronize the timing of the two events. There
are a number of plant species (not all of them shrubs) which depend,
partly or entirely, on hummingbirds for pollination. Jim Pojar,
well-known B.C. plant ecologist, wrote a scientific paper quite a few
years ago in SYESIS, the now-defunct journal of the B.C. Provincial
Museum, on coevolution of hummingbirds and their food plants. He
described 9 species of plants in B.C. which seem to be mainly
hummingbird-pollinated. The list includes salmonberry, red-flowering
currant, and black twinberry.

In B.C., plants like salmonberry NEED hummingbirds. No
hummingbirds, little or no pollination, and no reproduction. Likewise,
the hummers need the salmonberry to provide nectar on their northward
migration. There would be powerful natural selection against hummers
that arrived before flowers (and nectar) were available, and against
plants that consistently flowered before their pollinators had
arrived. There are lots of examples of coevolution between plants and
their insect pollinators, involving anatomical specialization as well
as synchronization of life cycles. It should not surprise anyone that
the same could apply to hummingbirds.

This certainly is not the whole story. Rufous Hummingbirds are
common migrants and breeders east of the Cascades in both Oregon and
B.C., where salmonberry and red-flowering currant are rare or absent.
I don't know what their main nectar sources would be there in the
spring migration. However, in B.C. at least, the arrival of Rufous
Hummingbirds east of the Cascades is more than a month later than on
the south coast. The average arrival date in the Okanagan Valley,
according to Cannings et al. (Birds of the Okanagan Valley, 1987) is
April 28 (46 years' records), compared to March 20 at Vancouver.
Surely, there is more than photoperiod involved here. Few other
species show such a huge discrepancy in arrival times east and west of
the Cascades. For example, Violet-green Swallows arrive only a week
later in the Okanagan Valley than at Vancouver (March 12 versus March
5).

Dennis Vroman mentioned manzanita as an important hummingbird
flower in southwestern Oregon. I think it would be worthwhile for
observers to record the native flower species that Rufous Hummers are
feeding from, especially when they first arrive, and especially east
of the Cascades. I think Dennis is also right when he talks about the
normal distribution, or "bell-shaped curve" of arrival dates-- that
birds arriving earliest are at greatest risk of perishing, and that
the peak arrival should coincide with peak flowering of
hummingbird-adapted flower species.

But enough for now. Does anyone else have comments, especially
anyone who has made particular studies of hummingbirds?

Wayne Weber
Kamloops, B.C.
wayne_weber at bc.sympatico.ca


-----Original Message-----
From: Mike Patterson <celata at pacifier.com>
To: Multiple recipients of list OBOL <OBOL at BOBO.NWS.ORST.EDU>
Date: Saturday, February 05, 2000 4:29 PM
Subject: Re: EARLY SPRING ARRIVALS: HUMMERS, SWALLOWS, VULTURES


>Salmonberry and currant are important early forage crops for
>hummingbirds, but hummingbirds along the Oregon Coast arrive
>well in advance of blooming of either of these species and
>they arrive because of day length not because the flowers
>have bloomed.
>
>The literature is rife with this statement about flowering
>plants as if the birds can somehow sense when the flowers
>are coming into bloom. Flower blooming and hummingbird
>arrival are closely synchronized events, both controlled
>by daylength and they have come to be so timed by natural
>selection. But in the case of hummingbirds, the northward
>movement, latitude by latitude is ahead of most bud burst.
>
>Here's an experiment: Let's inventory flowering plants
>when we hear about the arrival of hummingbirds in our
>area. I predict that latitudinal arrival occurs before
>significant blooming mostly along the coast and western
>interior valleys (this is my hypothesis). Further (second
>hypothesis requiring a different data analysis) longitudinal
>dispersal will be more closely correlated to flower blooms.
>
>And now all us citizen scientists have something to test
>through observation and experiment.
>
>My Theoretical Model: Hummingbirds arrive in our area
>before the food source along routes where the weather
>is, on average, mildest and disperse into less temperate
>areas as the conditions change.
>
>And the beauty is: I could be wrong and if I am we all still
>learn something.
>
>
>WAYNE WEBER wrote:
>
>> The arrival of Rufous Hummers in southwest B.C. seems to be
timed
>> to the flowering of Salmonberry (Rubus spectabilis) and
Red-flowering
>> Currant (Ribes sanguineum), whose flowers are major food sources
for
>> hummers. Salmonberry is noted for its long flowering season, with
some
>> plants always in bloom by late March, but most not reaching full
bloom
>> till well into April. If most of the Rufous Hummers arrived here
in
>> late March, they'd probably starve.
>>
>
>
>--
>Mike Patterson Alas, to wear the mantle of Galileo,
>Astoria, OR it is not enough to be persecuted
>celata at pacifier.com by an unkind establishment,
> you must also be right.
> ---Robert Park
>http://www.pacifier.com/~mpatters/bird/bird.html
>